On 7/10/23 17:08, Tejun Heo wrote:
Hello, Waiman.
I applied the prep patches. They look good on their own.
On Tue, Jun 27, 2023 at 10:34:59AM -0400, Waiman Long wrote:
...
cpuset. Unlike "cpuset.cpus", invalid input to "cpuset.cpus.exclusive"
will be rejected with an error. This new control file has no effect on
We cannot maintain this as an invariant tho, right? For example, what
happens when a parent cgroup later wants to withdraw a CPU from its
cpuset.cpus which should always be allowed regardless of what its
descendants are doing? Even with cpus.exclusive itself, I think it'd be
important to always allow ancestors to be able to withdraw from the
commitment as with other resources. I suppose one can argue that giving
exclusive access to CPUs is a special case which doesn't follow this rule
but cpus.exclusive having to be nested inside cpus which is subject to that
rule makes that combination too contorted.
Would it be difficult to follow how isolation modes behave when the target
configuration can't be achieved?
I would like to clarify that withdrawal of CPUs from
cpuset.cpus.exclusive is always allowed. It is the addition of CPUs not
presents in cpuset.cpus that will be rejected. The invariant is that
cpuset.cpus.exclusive must always be a subset of cpuset.cpus. Any change
that violates this rule is not allowed. Alternately I can silently
dropped the offending CPUs without returning an error, but that may
surprise users.
BTW, withdrawal of CPUs from cpuset.cpus will also withdraw them from
cpuset.cpus.exclusive, if present. This allows the partition code to use
cpuset.cpus.exclusive directly to determine the allowable exclusive CPUs
without doing an intersection with cpuset.cpus each time it is used.
Please let me know if you want a different behavior.
Cheers,
Longman
